Punch configuration

ABSTRACT

Punch configuration in which the geometry of the face involves planar surfaces which angle inwardly on opposed edges of the punch face. The angled planar surfaces terminate on a straight line and are interconnected by a grooved circular surface. As designed the punch configuration is symmetrical and the angles of the planar surfaces as well as the radius of the grooved cylindrical surface are calculated to require the least amount of punch force.

United States Patent McCutcheon [54] PUNCH CONFIGURATION [72] Inventor: Homer W. McCutcheon, Seattle, Wash. [73] Assignee: Telly Corporation, Seattle, Wash.

[22] Filed: Aug. 10, 1970.

211 Appl, No.: 62,333

52] us. Cl ..83/689 [51] Int.Cl. ..B26f 1/14 [58] Field of Search ..83/684-689;

' 30/315 [56] 1 References Cited UNITED STATES PATENTS 2,369,896 2/1945 Harris ..83/686 X [15,] 3,656,394 [4 1 Apr. 18,1972

3,504,588 4/ l 970 Thomas ..83/689 X Primary Examiner-Andrew R. J uhasz Assistant Examiner-David R. Melton Attorney-Graybeal, Cole & Barnard 5 7] ABSTRACT Punch configuration in which the geometry of the face in-' volves planar surfaces which angle inwardly on opposed edges of thepunch face. The angled planar surfaces terminate on a straight line and are interconnected by a grooved circular surface. As designed the punch configuration is symmetrical and the angles of the planar surfaces as well as the radius of the grooved cylindrical surface are calculated to require the least amount of punch force.

14 Claims, 9 Drawing Figures PATENTEDAFR 18 I972 sum NF 2 FIG-=4- PUNCHED \YET 10 BE CUT STAGE 3 STAGEZ P ucHi e a (ANGLED) YPE I; u T HOMER W.McCUTOHEO 5 INVENTOR.

STAGE l ATTORNEYS PATENTEDIPII I8 I972 656,894

SHEET 2 BF 2 "g TYPICAL ANGLED PIN .8

s=o(HERE) .7 NATI IAL 6 FMAXIFO a .5 V/i T DIE PLATE O i i i i 511'. I :3.-:'; r 0 l I 2 3 4 5 6 7 4 I oL=PUNCH PIN ANGLE DEGREES r HEEL MATERIAL m YET TO A BE CUT L T 1 L V fTJI ass WT ITW f .R I L sTAGEI STAGE2 STAGE3 y W 7 TYPE I PuNcHING (GROOVED) A H T AL H A a .7 (GRo'ovE) .51 v, i

if 7 I o .6- /I R WITHOUT 5 ANGLE o [\C *IR SHEAR IHEIGHT a I w--' MG 9 --f R MATERIAL -l5 HOMER \MMcOUTCHEON INVENTOR.

BY MAM o .65 .'I .I'5 FIG: 8

GROOVE RADIUS (R INCHES ATTORNEYS The invention relates generally to the art of punches and punch pins and more specifically to the geometry of the punch or punch-pin face. Essentially it is a device wherein the cutting edge of the male tool is so constructed that in its intended operation the work initially, will be engaged by a portiononly of the punch edges, with otheredge portions then necessarily engaging the work until the punching operation is completed.

As those skilled in the various punching arts are aware, known punch configurations have various drawbacks. These problems are encountered whether the artconcerns high speed punching of media such as paper or mylar tapes or whether it is involved with othermaterials suchas sheet metal, leather, plastic films, cardboard, or. plate. In practically all instances it is desirable to design the punching. apparatus so that the applied punch forces are as uniform as possible in order to avoid shock, impact or jerks. Such shock or impact punching forces inevitably shorten the life of the punch machinery. For instance in high speed punching operations such, as for paper and mylar tapes, excessive shock or impact loads damage the mechanism because of the high force demands on the low mass, high speed parts ln conventional punch design a cylindrically grooved pin provides the best punching characteristics but has short life since it wears out quickly and breaks easily at the fragile tips. On the other hand a single angled punch face may have greaterlife but because it is unsymmetrical, excessive side loading results which wears out the female die and the pins cutting edge. Additionallya dual or V-angled punch face requires very high forces toward the end of its punching cycle which is also undesirable.

Several prior art patents have been located which are of in-' terest but none shows the configuration or profile of this invention. Among the prior art references are US. Pat. Nos. 3,320,843; 3,176,570; 2,287,168; 3,334,809; 3,393,550 and French Pat. No. 592,179. All of the ennumerated references are to unrelated punch tip designs.

SUMMARY OF THE INVENTION The punch face geometry or configuration of this invention is mathematically defined. On the face of the punch at symmetrically opposed edges are provided inwardly angling planar surfaces having a mathematically predetermined angle. Each of the planar surfaces terminates inwardly of the edge along a straight transition line. The lines are joined by a cylindrically grooved surface the radius of which is also mathematically predetermined. Thus, there is provided a contiguous cutting action, part of which is done by angled edges and part of which is accomplished by a cylindrically grooved edge.

Accordingly it is among the many features, objects, and advantages of this invention to provide a punch and punch-pin configuration which functions reliably at high speeds with very low forces and reduced wearr'lhe invention, the geometry of which is mathematically defined, provides a continuous force transition throughout all stages of the punching cutting stroke.

The invention provides sharp edge entry at a controllable angle, the angle being calculated to maximize resistance of the punch to wear and to provide good impact resistance. The configuration of this invention can be applied to any generally round, square, multi-sided or, rectangular punch with similar results. The configuration of this punch gives unique total cutting edge by providing a low shear height not available in existing total low force punch pins. The invention affords minimum stroke length and thus higher speed operation with reduced wear on both the punch pin and the die block. This punch shape can easily be generated or defined in highly wearresistant materials such as carbides for sustained useful life during, for example, punching of highly abrasive media. The lower punch forces required by this design reduce inputpower from the actuating mechanism and thus the actuating mechanism itself can be of lower mass again contributing to higher speed operation. The radius of the cylindrically 2 grooved surface and the angle of the planar surfaces may be mathematically chosen to provide optimum transitions for given punch diameters.

BRIEF DESCRIPTION OF THE DRAWINGS surfaces being somewhat exaggerated for the purposes of effective illustration;

FIG. 2 is a side elevational' view of the punch of FIG. 1

' further illustrating the symmetrical configuration of the punch FIG. 3 shows a partial perspective view of a rectangular punch tool having the geometry of this invention, the surfaces of which also have been drawn out of proportion in order to illustrate the principles of the invention;

FIG. 4 is a side elevational view of the punch of FIG. 3 illustrating the design profile thereof;

FIG. 5 is a series of three views illustrating principle of single angled punch faces;

FIG. 6 shows a curve plotting dimensionless force ratio requirements against face angles for a typical single angled pin configuration; I

FIG. 7 is a series of three views illustrating cylindrically the punching grooved pin punching principles of operation;

FIG. 8 is a curve plotting dimensionless force ratio against groove surface radii for a typical grooved punch configuration; and

FIG. 9 is a comparative diagr'amatic view of a conventional grooved configuration versus the geometry of the instant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS I In general there are two types of shearing action which are 7 .relatedto the shear height (H) chosen for the cutting edge of a punch. Type I shearing action as shown in FIG. 5, is defined for cases in which the material thickness is greater than the total shear height (I 2 IL) and indicates that the trailing edge or heel of the punch comes into contact with the top surface of the material being punched before the leading edge or toe exits from the bottom of the material. In the case where material thickness is less than total shear height (I s H.) we have what is referred to as Type II action in which toe" exits prior to heel" contact with the material.

In the instant situation two distinct cutting actions are designed into the punch face. If one looked at the angled surfaces alone it would be concluded that a Type I situation exists for small angles a. Simularly if the grooved surface with its low maximum punch force was used alone it would lead one to assume a Type II action exists. The pin face of this invention, however, uniquely transfers from the Type I situation to the Type II situation at the line of intersection or transition where the angled planar surfaces meet the cylindrically grooved surface. "Ihe analysis which follows hereinafter assumes, for purposes of continuous and smooth force transmission and contiguous cutting action, that the Type I, Stage 2, cutting action exists instantaneously both for the angled planes and the cylindrical groove at these lines of planar surface intersections with the groove. The reason for making this assumption is that at the lines of planar intersection the cutting actions transfer from a Type I to a Type II action. It is necessary therefore to simplify the solution to the mathematical equations which define the punch force at the intersection of the two dissimilar surfaces. Essentially we are solving two equations simultaneangled cutting edges. The graph of FIG. 6 shows that small changes in angle a, for small t/R in which I is material thickness and R is punch radius, can produce large decreases in maximum force. If angled pins alone are used the die is subjected to considerable side loading due to the non-normal or unsymmetrical punching loads. Further, removal of punched out material is not efficient. However this general configuration, that is a typical small angled pin, gives very good tip strength which in turn results in the punch having high wearresistance at its tip. The data for the curve in FIG. 6 was computed on the basis of S/t l to show the eflects of angle change in the worst or highest force requirement situation, for the given Type I punching action chosen. The term S herein denotes the distance between the punch toe and the top of the material being punched.

The following mathematical equations are used to solve for the dimensionless force ratio by arbitrarily selecting angles a for a given pin size and then plotting these angles versus the dimensionless force ratio. Note that the lower the dimensionless force ratio the lower the expected punch force will be. For the angled pin, the pin diameter 2R, t material thickness and 'r material shear strength. These factors enable computation of the maximum force or F,,= 2 1- 1r Rt.

In the Type I situation for a condition in which S/t l we have the following formula with which to calculate F /F The equation is:

'dIlLY Along with the desirable characteristics of the angled pin it is desirable to produce low force punching. Also it is desired that there be provided a means for equally distributing the punching forces to effect minimum side wear and reduced friction forces. Furthermore, it is preferred to have a configuration which is economical to produce and has a minimum shear height.

Recognizing the advantages of the angled punch face alone, which include initial low punch force in Stage 1, it becomes desirable to contiguously continue the low punch force in all stages of the punching. Of the possible shapes from which to choose, the cylindrically grooved configuration appears to be optimum for continuation of the low punch forces. The proper cylindrical shape must be selected to provide a uniform, continuous, punch load transition from the planar surface to the cylindrical surface. As mentioned above this is essential in order to minimize shock loads to the punch drive mechanism. Providing an angled planar surface on one side of the punch is not adequate, so in order to escape the drawbacks of the typical single angled pin there is provided a symmetrical face with planar angled surfaces on each side. Again, and with reference to FIGS. 7 and 8, the shape required can and must be mathematically defined to provide optimum low punch force. Type I punching is again selected for the groove surface at its instantaneous line of action as it was for the angled surfaces. In like manner, then, for the cylindrical groove shape the following equation is used to plot the dimensionless force ratio versus the range of arbitrarily selected radii. In this instance z/ R 2 C C 1 in which C R /R. The curve of FIG. 8 shows the dimensionless force ratio F /F plotted versus several R assuming the same diameter pin and material thickness as with the angled pin illustration. The equations for Stage 2 cylindrically grooved punching, in which 3/! l are:

In these equations R pin radius, t= material thickness, C R /R, R groove surface radius, S distance between toe of the punch and the top of the material, F force for a given pin, and F, 2r1rRt.

Referring now to the graphs in FIGS. 6 and 8 it will be seen that the F /F on the vertical axis of the graphs defines a shaded area which when extended to the curve defines an optimum angle range for the planar surfaces and an optimum range of radii for the cylindrical groove. The cutting action of the edges of this new punch pin consist of two separate contiguous actions wherein the first stage has been penetration" or the onset of cutting which proceeds along the dual planar edges defined by the angle a. By the time the point or transition line at which the cylindrical groove surface will begin cutting, the cutting action may be assumed to be a Stage 2 situation, represented in the equations for the cylindrical surface above.

It will thus be seen that a radius R,,, and an angle a can be selected from the curves such that the force ratios for both types of surfaces are identical or nearly so. This provides a continuous force action. Furthermore, the force ratios can be selected to a low magnitude which means that the punching forces will be minimal. Still further, it means that even though there are two distinct types of punching action there is a con- 1 tinuous, contiguous, low force, low wear, symmetrically loaded punch shearing action.

Geometrically, the range of R and 01 available for selection permits the use of the unique punch face geometry on most sizes of generally round, square, rectangular and other shapes of punches. The shear height H of the pin can be calculated once the angle a and the cylindrical radius R have been selected for a given sized pin. In this case the total shear H equals the height Ha of the planar surfaces plus height H, of the grooved surface. Ha is calculated by the equation Ha (L) tan a and H is calculated by the equation H =R l cos (arcsin R/R,,)]. Another feature, illustrated in FIG. 9, is that the geometry or configuration of this punch is such that it minimizes the required shear height H. In all situations the new punch configuration of this invention affords minimum shear height while simultaneously providing for minimum punching forces when compared to the cylindrically grooved pin. Note that with the geometry of this invention total shear height H is less than the total shear height of a standard cylindrically grooved punch with equivalent punch force requirement. The new geometry is shown in solid lines in FIG. 9 while the shear height of conventional groove punches is shown in the same FIG. in dotted lines. For planar surfaces a bearing stress analysis is conducted to determine that the applied forces will not exceed the stress limits of the punch material.

Referring now to FIGS. 1 and 2 it will be seen that there is a round punch generally designated by the number 10. The punch has opposed angled planar surfaces 12 formed at angle a. The punch also has cylindrical surface 14 with radius R,,. The cylindrical surface 14 intersects the opposed angled planar surfaces at the transition edges 15. For purposes of illustration only, and to indicate further that the respective planar and cylindrical surfaces are out of proportion, a .0720 diameter punch may have planar surfaces 12 with minimum width of about .003 inch. The radius R, of the cylindrical surface will be approximately .060 inches. The angle of planar surfaces 12 will be about 6. Thus in a very small diameter punch pin surfaces 12 could be nearly invisible to the naked eye.

Formation of planar surfaces 12 defines cutting edges 11 on the periphery of the punch body which extend down and away from the diameter line. Cutting edges 11 terminate at both ends of transition edges 15 or points 13. The cylindrically grooved surface then generates cutting edges 17 extending between opposed points 13 on the same side of the punch. Accordingly it will be understood that an essentially mathematically defined planar surface 12 develops an essentially curved cutting edge 11 with the outer surface of body 10. Such cutting edge 11 is equivalent to the curved cutting edge 17 generated by a cylindrically grooved surface and therefore produces the same low force punch profile but with good wear resistance which does not exist with the conventional grooved profile. Thus the cutting action proceeds with the entrance of the highest area of cutting edges 11 entering the material and progressing along both sides of each of edges 11 to points 13. Cutting edges 17 then take over the punching action until the lowest areas of edges 17 have emerged from the material.

In like manner FIGS. 3 and 4 show rectangular punch 20 having opposed angled planar surfaces 22 with angle a, and cylindrical surface 24 having radius of curvature R,,. The planar surfaces 22 intersect the grooved surface 24 at transition lines 26. Surfaces 22 define first cutting edges 23 and a pair of second cutting edges 25 terminating at the ends of transition lines 26 or points 27. The grooved surface then defines cutting edges 28 extending between points 27.

It is to be understood that other mathematical formulas may be used or considered in the design of this shape. Further there exists an infinite number of instantaneous solutions to the mathematics illustrated for selecting this general punch shape. While fiat planar surfaces are the preferred form of the invention it is possible to make these surfaces either convex or cancave. A concave surface, however, is least likely since it is subject to the disadvantages of a conventionally designed grooved surface. Additionally it is possible to form more than two planar surfaces in a given punch although machining considerations become quite complex.

[claims 1. A punch configuration for punching, holes in materials, comprising:

a. a punch body having a material engaging end,

b. said end being defined by generally symmetrically opposed surfaces extending inwardly at a predetermined angle for a predetermined distance with each of said surfaces defining a first cutting edge, each of said surfaces terminating so as to form opposed transition edges,

0. a grooved cylindrical surface extending between said opposed transition edges and having a predetermined radius of curvature defining second cutting edges extending between the ends of said transition edges.

2. The punch configuration according to claim 1 and wherein said first cutting edges have a highest portion which extends inwardly and downwardly away from said highest portion to the ends of said transition edges.

3. The punch configuration according to claim 2 and wherein said opposed surfaces are generally planar and generally of the same dimensions.

4. The punch configuration according to claim 3 and in which said transition edges are generally parallel.

5. The punch configuration according to claim 4 and in which the angle of said planar surfaces and the radius of said grooved cylindrical surface are formed to provide a substancutting and shearing contiguous cutting action requiring approximately the same punching forces as punching transfers from the first cutting edges of the planar surfaces to the second cutting edges of the grooved surface.

6. The punch configuration according to claim 5 and in which the highest portion of said first cutting edges lie in ap proximately the same plane wherein said plane is disposed normal to the longitudinal axis of said body.

7. The punch configuration according to claim 6 and wherein said transition edges lie in approximately the same plane wherein said plane is disposed normal to the longitudinal axis of said body.

8. A punch configuration for punching, holes in materials, comprising:

a. a punch body having a material engaging end,

b. said end being defined by a pair of generally symmetrically opposed spaced apart surfaces extending inwardly at a predetermined angle for a predetennined distance with each of said surfaces together with the outer surface of said body defining a first cutting edge, each of said surfaces terminating so as to form opposed, spaced apart transition ed es, a grooved cy lndrical surface extending between said opposed transition edges and having a predetermined radius of curvature and together with the outer surface of said body defining second cutting edges extending between the ends of said transition edges.

9. The punch configuration according to claim 8 and wherein said first cutting edges have a highest portion which extends inwardly and downwardly away from said highest portion to the ends of said transition edges.

10. The punch configuration according to claim 9 and wherein said opposed surfaces are generally planar and generally of the same dimensions.

11. The punch configuration according to claim 10 and in which said transition edges are generally parallel.

12. The punch configuration according to claim 11 and in which the angle of said planar surfaces and the radius of said grooved cylindrical surface are formed to provide a substantially continuous, contiguous cutting action requiring approximately the same punching forces as punching transfers from the first cutting edges of the planar surfaces to the second cutting edges of the grooved surface.

13. The punch configuration according to claim 12 and in which the highest portion of said first cutting edges lie in approximately the same plane wherein said plane is disposed normal to the longitudinal axis of said body.

14. The punch configuration according to claim 13 and wherein said transition edges lie in approximately the same plane wherein said plane is disposed normal to the longitudinal axis of said body.

tially continuous,

cutting and shearing 

1. A punch configuration for punching, cutting and shearing holes in materials, comprising: a. a punch body having a material engaging end, b. said end being defined by generally symmetrically opposed surfaces extending inwardly at a predetermined angle for a predetermined distance with each of said surfaces defining a first cutting edge, each of said surfaces terminating so as to form opposed transition edges, c. a grooved cylindrical surface extending between said opposed transition edges and having a predetermined radius of curvature defining second cutting edges extending between the ends of said transition edges.
 2. The punch configuration according to claim 1 and wherein said first cutting edges have a highest portion which extends inwardly and downwardly away from said highest portion to the ends of said transition edges.
 3. The punch configuration according to claim 2 and wherein said opposed surfaces are generally planar and generally of the same dimensions.
 4. The punch configuration according to claim 3 and in which said transition edges are generally parallel.
 5. The punch configuration according to claim 4 and in which the angle of said planar surfaces and the radius of said grooved cylindrical surface are formed to provide a substantially continuous, contiguous cutting action requiring approximately the same punching forces as punching transfers from the first cutting edges of the planar surfaces to the second cutting edges of the grooved surface.
 6. The punch configuration according to claim 5 and in which the highest portion of said first cutting edges lie in approximately the same plane wherein said plane is disposed normal to the longitudinal axis of said body.
 7. The punch configuration according to claim 6 and wherein said transition edges lie in approximately the same plane wherein said plane is disposed normal to the longitudinal axis of said body.
 8. A punch configuration for punching, cutting and shearing holes in materials, comprising: a. a punch body having a material engaging end, b. said end being defined by a pair of generally symmetrically opposed spaced apart surfaces extending inwardly at a predetermined angle for a predetermined distance with each of said surfaces together with the outer surface of said body defining a first cutting edge, each of said surfaces terminating so as to form opposed, spaced apart transition edges, c. a grooved cylindrical surface extending between said opposed transition edges and having a predetermined radius of curvature and together with the outer surface of said body defining second cutting edges extending between the ends of said transition edges.
 9. The punch configuration according to claim 8 and wherein said first cutting edges have a highest portion which extends inwardly and downwardly away from said highest portion to the ends of said transition edges.
 10. The punch configuration according to claim 9 and wherein said opposed surfaces are generally planar and generally of the same dimensions.
 11. The punch configuration according to claim 10 and in which said transition edges are generally parallel.
 12. The punch configuration according to claim 11 and in which the angle of said planar surfaces and the radius of said grooved cylindrical surface are formed to provide a substantially continuous, contiguous cutting action requiring approximately the same punching forces as punching transfers from the first cutting edges of the planar surfaces to the second cutting edges of the grooved surface.
 13. The punch configuration according to claim 12 and in which the highest portion of said first cutting edges lie in approximately the same plane wherein said plane is disposed normal to the longitudinal axis of said body.
 14. The punch configuration according to claim 13 and wherein said transition edges lie in approximately the same plane wherein said plane is disposed normal to the longitudinal axis of said body. 